This invention relates to a fuel control system for controlling the fuel flow of a compression ignition engine and more particularly to an altitude compensated device for adjusting the maximum fuel flow delivery to the engine with changes in altitude.
Compression ignition engines commonly utilize fuel injection systems for delivering fuel to the combustion chambers. With such fuel injection systems, a metered amount of fuel is delivered to the combustion chambers in accordance with the setting of a fuel pump feed rack which is normally controlled by a governor. A fixed full load rack stop is normally provided to limit the maximum volume of fuel directed to the engine for establishing the full load speed of the engine. One of the problems frequently encountered with such fuel systems is that the rack stop is normally set for a predetermined altitude range so that all fuel delivered to the combustion chambers is efficiently and completely burned. However, trucks having compression ignition engines frequently operate in both high altitude mountainous areas and low altitude plain areas. When the maximum fuel deivery is adjusted for low altitude conditions, excessive smoke is produced at the higher altitudes due to difference in air-fuel ratios. Conversely, when the maximum fuel delivery is adjusted for high altitude conditions the engine does not develop its maximum horse power capability at the lower altitudes.